1. Field of the Invention
The present invention relates to a merged MR head made by notching the first pole piece of the head""s write element with a notching layer, and also to forming a notched first pole piece with a first pole piece layer and the notching layer, and then milling a second pole piece layer, a gap layer and the notching layer until side walls of the second pole piece layer, gap layer and notching layer are contiguous.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap that is recessed from the ABS. The first and second pole pieces have first and second pole tips, respectively, which terminate at the ABS. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces, and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces write fields in the first and second pole pieces. A non-magnetic gap layer is sandwiched between the first and second pole tips. Write fields of the first and second pole tips at the ABS fringe across the gap layer. In a magnetic disk drive, a magnetic disk is rotated adjacent to, and a short distance (fly height) from, the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain information in the form of magnetized segments with fields detectable by the MR read head.
The MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers, and located at the ABS. The first and second gap layers and the MR sensor are sandwiched between first and second shield layers. In a merged MR head, the second shield layer and the first pole piece are a common layer. The MR sensor detects magnetic fields from the rotating disk by a change in resistance that corresponds to the strength of the fields. A sense current is conducted through the MR sensor, where changed in resistance cause voltage changes that are received by the processing circuitry as readback signals. One or more merged MR heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk.
Good design dictates that the write head writes with a wide track profile, while the read head reads a more narrow track profile in order that the read head not pick up signals from adjacent tracks in the presence of track misregistration. Signals picked up from adjacent tracks result in poor readback performance. The write head is also employed to write servo signals on the magnetic disk, in spaced apart sectors dedicated for servo signals. The disk typically has allocated regions dedicated for the imbedded servo information. The servo signals are read by the read head and employed by servo processing circuitry to maintain the write head on track.
In the prior art, the first pole piece layer of the write head has been notched to improve its servo writing performance. The notching forms a portion of the first pole piece into a pedestal with first and second side walls that align with first and second side walls of the second pole tip. With notching, the fringe field at the gap between the second pole tip and the first pole piece is limited to the width of the second pole tip, which defines the width of tracks written on a disk. This is because the field is captured by the pedestal instead of spreading out laterally to the flat portion of the first pole piece on each side of the second pole tip. Accordingly, tracks on the magnetic disk have narrow erase bands. From a servo perspective, narrow erase bands improve the quality of the servo pattern which consists of phase aligned transitions. However, data tracks favor wider erase bands which diminishes interference from adjacent tracks in the presence of track misregistration. Since servoing cannot be sacrificed, there is a strong felt need for a write head that writes good servo tracks, but is better than the prior art at writing data tracks.
Typically, a second pole piece, along with its second pole tip, is constructed by frame-plating it on top of the gap layer. After depositing a seed layer on the gap layer, a photoresist layer is spun on the seed layer, imaged with light, and developed to provide an opening surrounded by a resist wall for plating the second pole piece with its second pole tip. To produce a second pole tip with a narrow track width, the photo-resist layer has to be relatively thin. This relationship, referred to as the xe2x80x9caspect ratioxe2x80x9d, is the ratio of the thickness of the photoresist layer in the pole tip region to the track width of the second pole tip. Preferably, the aspect ratio should be on the order of three. In other words, for a track width of 1 xcexcm, the thickness of the photoresist in the pole tip region should be about 3 xcexcm. If the photoresist is thicker than this, the side walls of the second pole tip, especially at the base, will not be well formed due to scattering of light as it penetrates the photoresist layer during the imaging step.
A prior art process for notching the first pole piece entails ion beam milling the gap layer and the first pole piece, employing the second pole tip as a mask. According to this prior art process (typified in U.S. Pat. No. 5,452,164 and U.S. Pat. No. 5,438,747), a full film gap layer is formed on a first pole piece layer, followed by frame plating a second pole piece layer and pole tip on the gap layer. The second pole tip layer is employed as a mask during milling of notches in the second pole tip layer. The direction of milling beam forms an angle to a vertical axis while the workpiece is rotated. The procedure first mills through the gap layer, and next mills the first pole piece layer to form the notches. Since each notch site is directly below a respective side wall of the second pole tip, each notch site is milled for about 180xc2x0 of the rotation, and then is shadowed by the second pole tip, preventing milling for the next 180xc2x0 of rotation.
In order to account for windage (material consumed by processing), the second pole tip is frame plated, wider than a desired target track width, and thicker than a desired height. During milling of the gap layer to form the write gap, the top and first and second side walls of the plated second pole tip layer are partially consumed. During milling of the first pole piece layer to form the notches, the top and first and second side walls of the second pole tip layer are still further partially consumed. During both milling times, milled material is redeposited on the side walls of the second pole tip. This is removed by angling the milling beam closer to a normal to the side walls. This process, referred to as clean-up, requires extra milling time. Because of the long processing time and large windage of the second pole tip it is difficult to keep the track width and the pole tip height within acceptable limits. When the limits are exceeded, a wafer with literally thousands of magnetic head sites must be discarded. Further, increasing the height of the plated second pole tip layer to account for windage, increases the aforementioned aspect ratios, making it difficult to construct a well-defined second pole tip with a submicron track width. Track widths 1 xcexcm or less are desirable to increase tracks per inch (TPI) written on the disk.
Accordingly, there is a strong felt need to reduce the processing time required for notching, without sacrificing narrow track widths and quality of the write head.
We have discovered that a single-sided, notched write head writes narrow erase band servo tracks equally well as a double-notched write head since the servo pattern is written with only one side of the write head. This produces a superior servo pattern compared to the conventional merge write head. For data performance, this implies that the single sided notch head is not as good as the merged head for mitigating side interference, but is better than the dual-sided notched write head. The single-sided notched write head will write a narrow erase band on the notched side and a wide erase band on the side that is not notched. In one embodiment, only one side of the first pole piece layer is notched, and in another embodiment, a first side of the first pole piece layer is notched more than a second side thereof. In operation, the single-sided, notched write head is moved a distance less than the track width of the write head for each servo track written on the disk. For instance, if the write head is moved over one-half a track width for each servo track, servo tracks can be written with a narrow erase band on each-side of each servo track. Accordingly, the single-sided, notched write head can write servo tracks equally well as a double-sided, notched write head. Data tracks will be written with a narrow erase band on one side and a wide erase band on the other side. This is a better configuration for read head performance than one with a narrow erase band on both sides of the data track. The wide erase band on one side of the data track allows greater flexibility in spacing the read head from adjacent tracks.
The construction of a single-sided, notched write head requires less time to construct than a double-sided, notched write head. We have provided several methods of construction. Generally, the windage of the second pole tip can be reduced by {square root over (2)}. In one method, the second pole tip is frame-plated on the gap layer, and photoresist is employed for protecting a side of the first pole piece layer that is not to be notched. Milling is then employed for notching only one side of the first pole piece layer. With this arrangement, there is less redeposition since material on only one side is milled. Accordingly, the milling time necessary for clean-up is shortened. Further, the workpiece can be oscillated back and forth 180xc2x0 so that the notch site is literally constantly milled, without being shadowed during 180xc2x0 of the rotation. The processing time is significantly reduced, reducing the windage of the second pole tip. As stated hereinabove, less windage keeps the desired track width and pole tip height within acceptable limits. The method promotes constructing second pole tips with a track width of 1 xcexcm or less. Another method employs a notching layer on top of the first pole piece layer. The notching layer is slightly wider than the target track width, on the side to be notched, and has a wide lateral expanse, on the side that is not to be notched. On the side to be notched, a small corner of the notching layer is exposed beyond the second pole tip. Upon rotating the workpiece, the small corner is quickly milled away while the large expanse of the notching layer on the other side of the second pole tip is only slightly notched. This produces an embodiment of the invention where one side of the first pole piece layer is notched significantly more than the other side.
An object of the present invention is to provide a single-sided, notched write head that has the same servo writing capability as a double-notched write head, but improved data writing capability.
Another object is to provide a method of making a notched write head that requires less processing time than a double-notched write head for the purpose of constructing a second pole tip with a track width of 1 xcexcm or less.
A further object is to provide a notched write head that has a better-defined, and narrower, second pole tip than a double-notched write head.
Yet another object is to provide a method of notching a first pole piece with more control of the target height and target track width of the second pole tip.
Still another object is to provide a method of notching a first pole piece of a write head with less consumption of a second pole tip, and with less redeposited material to clean up after the notching.
Still a further object is to provide a method wherein single-sided notching of a write head can be performed.
Still another object is to provide a single-sided, notched write head that writes narrow erase band servo tracks equally as well as a double-notched write head, writes data tracks better than a double-notched write head, and requires less time to produce than a double-notched write head.